1. Field of the Invention
This invention relates generally to an electronic circuit for interfacing a telephone handset to a telephone base unit and, more particularly, to an electronic circuit for interfacing a variety of different telephone handsets to different types of telephone equipment.
2. Description of the Related Art
There exists a great variety of telephone equipment and peripheral devices, such as telephone handsets. Most handsets are made to conform to certain telephone system standards. For example, telephone handsets are normally equipped with carbon, electret, or dynamic type transducers.
Carbon, electret, and dynamic transducers have different electrical characteristics, such as impedance, demand on bias current, and signal magnitude that can vary by as much as 40-60 dB. Telephone handsets are, therefore, equipped with transducers that match their electrical characteristics with the electrical characteristics of the instruments with which the handsets are intended to be used, such as the base unit of a telephone. If telephone handsets are connected to incompatible instruments, unpredictable performance may result, i.e. excess noise, reduced quality of transmissions, etc.
It has been common practice to receive electrical power for the telephone and associated equipment directly from the telephone lines. However, increasingly sophisticated electronics in the telephones have increased the demand for electrical power beyond that available from the telephone lines. Accordingly, transmission quality is in danger of being significantly reduced. Hence, the trend is toward AC and battery powered telephones and peripheral equipment. However, neither AC nor battery power offers an ideal solution. Rather, both suffer from inherent shortcomings.
For example, AC power is not always readily available. Similarly, batteries need to be checked and replaced at relatively frequent intervals; an operation regarded as bothersome by most users.
The present invention is directed to overcoming one or more of the problems set forth above.